The feasibility of graft enhancement will be studied in rodent allograft and heterograft heart models. Graft prolongation by Dipyridamole will be attempted. The enhancement studies will include both active and passive enhancement protocols, with and without the addition of standard chemical immunosuppressive agents. After the effect of Dipyridamole on the clotting mechanism of the rat has been determined, the effect of this agent on allograft and xenograft survival will be studied. We will continue to study the mechanism of action of Concanavalin A in prolonging heart allografts.